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Full text of "Ensuring Rail Road Tank Car Safety"

Tank Car Design and Use Characteristics     41

EXPLANATION OF TANK CAR DESIGN

SPECIFICATION NUMBERS
(General American Transportation Corporation 1991)
DOT    111     A     60    AL    W

:       :         :        Welded construction
:       :      Construction metal other than steel (alumi-
:        :       num)
:      Tank test pressure
Insignificant unless S, T, or J (see below)
Class number
Authorizing agency

Authorizing Agency

Tank cars that meet DOT or AAR specifications are designated with the
appropriate specification number beginning with either prefix. AAR cars
meet most DOT requirements and are authorized to carry some regulated
commodities.

Class Number

Class numbers denote general categories of tank cars that have several
common design and construction features. The most common tank car is the
DOT-111, which accounts for about three-quarters of the tank car fleet. The
111, which is a nonpressure design, carries most kinds of materials moved by
tank car. The next most common classes are the DOT-105 and DOT-112
pressure tank cars, which account for between 20 and 25 percent of tank cars
in service and a higher share of tank cars used in hazardous materials service.

"A," "S," "J," and "T" Identifiers

The letters A, S, J, or T follow the class number of some tank car designs.
Whereas A has no special significance except as a separator of the class and
test pressure numbers, the other letters indicate that the car is equipped with
certain protective systems. S indicates that the car is equipped with head
protection. J indicates that the car is equipped with head protection and
jacketed thermal protection. T indicates that the car is equipped with head
protection and sprayed-on thermal protection. These designations apply
mainly to the pressure tank cars, which carry most of the commodities that
require the special protection.

Tank Test Pressure

For most tank cars, the tank test pressure is denoted in the specification
designation. Test pressures are measured in pounds per square inch (psi)
using test methods prescribed in the regulations. Test pressures generally
range from 60 psi (except in some older cars) for general service tank cars to
600 psi for the highest test-pressure cars. The Ills can be tested for 60 or
100 psi, although most new cars are built to the 100-psi specification. Most
new 105 and 112 cars are built to specifications of 300 psi or higher.